MLA

Williams, William Carlos, 1883-1963. The Kenyon Review. Box 9, folder 344. 1939-1956, undated. https://collections.library.yale.edu/catalog/17049496.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 9, folder 344"])(1939-1956, undated)[The Kenyon Review]. https://collections.library.yale.edu/catalog/17049496.